This invention relates to a control method for jet pressure of a picking nozzle in a loom and control apparatus therefor in which in a jet loom, even when the flying characteristic of filling yarns is varied, the stable picking operation may be continued.
In a jet loom, particularly in an air jet room, when the flying characteristic of filling yarns used for weaving is changed, picking sometimes becomes unstable. It is contemplated that such unstable picking principally results from the fact that air resistance changes since a variation in yarn properties such as coarseness of yarns, sizes of fuzz, etc. occurs lengthwise of the filling yarns.
In view of the foregoing, various procedures have been proposed in order to continuously perform stable picking operation even when the flying characteristic of the filling yarns is changed. In the most basic procedure, a mechanical angle of a loom (hereinafter referred to as an arrival angle of filling yarns) at which a filling yarn having a predetermined length has-been picked is monitored during picking to determine the variation of the flying characteristic of the filling yarn according to a detected change of the arrival angle, and the jet pressure of a main nozzle and a subnozzle (hereinafter referred to as a picking nozzle) for picking is controlled accordingly.
Thereby, when the flying characteristic of the filling yarn is declined and a delay of the arrival angle is detected, the jet pressure is controlled so as to be increased in order to correct it. On the other hand, for the advancement of the arrival angle, the jet pressure is controlled to be lowered whereby the arrival angle of the filling yarn is maintained to be constant.
In controlling the jet pressure of the picking nozzle as described above, when the jet pressure is set so as to be extremely high or conversely extremely low for some cause, broken yarns, short-picking, looseness, etc. sometimes occur. Therefore, it has been proposed to provide a suitable upper limit value and lower limit value for the control range of the jet pressure (for example, Japanese Patent Application Laid-Open (Kokai) No. 63(1988)-92753).
However, according to the prior art as described, there is a problem in that it is not always easy to determine a proper control range of the jet pressure. That is, generally, the flying characteristic of the filling yarns varies along with a yarn supply package and even one and the same supply package is different in flying characteristics in its outer layer portion and inner layer portion. Therefore, even if the upper limit value and lower limit value of the jet pressure are simply manually set, the jet pressure to be controlled is not always suited to the flying characteristic of the filling yarns being supplied. Accordingly, it is difficult to positively realize stable picking.
It is to be noted that the upper limit value of the jet pressure is sufficiently determined such that the occurrence of broken filling yarn does not occur, and therefore no significant problem will occur even if a fixed value is manually set. On the other hand, unless the lower limit value is set properly, the jet pressure cannot be sufficiently lowered. For this reason, the arrival angle becomes abnormally advanced or conversely the jet pressure is excessively lowered, possibly giving rise to occurrence of picking defects such as looseness, short-picking, etc.
Generally, when a jet pressure P of the picking is nozzle lowered, an arrival angle .theta.e increases its unevenness .DELTA..theta.e for each picking as shown in FIG. 6. Even if the average arrival angle .theta.e is not greatly varied from a target arrival angle .theta.eo, there is possibly exceeded an allowable arrival limit .DELTA..theta.eo momentarily due to the unevenness .DELTA..theta.e.